CMake: Support dynamic codegen outputs (#68246)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68246
Currently the codegen produces a list of output files at CMake
configuration time and the build system has no way of knowing if the
outputs change. So if that happens, you basically need to delete the
build folder and re-run from scratch.
Instead, this generates the output list every time the code generation
is run and changes the output to be a `.cmake` file that gets included
in the main cmake configuration step. That means the build system
knows to re-run cmake automatically if a new output is added. So, for
example you could change the number of shards that `Operators.cpp` is
split into and it all just works transparently to the user.
Test Plan: Imported from OSS
Reviewed By: zou3519
Differential Revision: D32596268
Pulled By: albanD
fbshipit-source-id: 15e0896aeaead90aed64b9c8fda70cf28fef13a2
